Android control for navigation

So this will probably be mostly to discuss this work and very likely won't get merged for some time.  This code creates hooks for a flight position mode on the transmitter which passes control to the tablet (connected via telemetry, so this could/should have a parallel implementation in GCS).  It supports things like enabling position hold,  return to home, return to tablet, etc.

I don't like this code getting dumped into the ManualControl module, nor do I like how much it ends up invading on the main manual control code.